1. Field of the Invention
The present invention relates to a digital camera which compensates defect pixels of a solid state imaging device, and a system for compensating defect pixels of a solid state imaging device.
2. Description Related to the Prior Art
In recent years, a digital camera having a solid state imaging device such as a CCD sensor or a CMOS sensor is used. Since such solid state imaging device has at least millions of pixels, it is practically difficult to produce the solid state imaging device with no defect pixel. Accordingly, there is a need to use the solid state imaging device in view of the presence of certain defect pixels.
The defect pixel is a pixel which does not output the signal correctly corresponding to subject brightness. For example, there are a white defect pixel which generates signal (charge) even when the light is not entered and a black defect pixel which does not generate signal (charge) even when the light is entered. The white defect makes a picture pixel brighter, and the black defect makes a picture pixel darker. To prevent a deterioration of image quality caused by the defect pixel, it is already developed a digital camera which compensates the signals of defect pixels by software process.
In digital cameras disclosed in Japanese Patent Laid-Open Publications No. 2000-059690 and No. 05-068209, defect pixels of a solid state imaging device are detected in a production process by a defect inspection machine. Then information of position, kind and degree of the defect of each defect pixel is stored for example in a memory incorporated in the digital camera. Accordingly, output signal of the defect pixel can be compensated by interpolating the output signal of the defect pixels with the output signal of surrounding normal pixels. The solid state imaging devices are expected to have more and more pixels, and therefore the accurate compensation of the defect pixels is essential to increase quality of product.
However, in the digital cameras disclosed in the Japanese Patent Laid-Open Publications No. 2000-059690 and No. 05-068209, although the defect pixels detected at a factory can be compensated, defect pixels newly generated by aging degradation of the solid state device after shipment cannot be compensated.